This invention relates to the frame that is mounted on the truck and supports the drum and auxiliary apparatus of a transit concrete mixer.
In a conventional transit concrete mixer, the mixer drum rests on pedestals which are mounted on the side sills or rails of the truck. One of the pedestals supports the closed end of the drum and the other, the open end of the drum through which material is charged and discharged.
Drum rotating means are frequently connected to a trunnion which extends axially from the closed head of the drum. The opposite end of the drum is provided with a track that rests on rollers mounted on a pedestal of the frame. The rollers serve as a cradle for the portion of the drum which rests on them.
Both pedestals include crossmembers and uprights members disposed to perform their function of supporting the drum. Power from the truck is customarily used to rotate the drum while the truck is transporting the mixer, and the mixer is either used to mix or agitate the concrete in the drum.
Present mixer drums are very large and impose a substantial load on the truck frame. Due to road irregularities, the truck frame is subjected to various strains and distortions including twisting action which in turn twists portions of the pedestals.
In addition, there is an angular difference between the left and right rails of the truck under certain load conditions causing a scissor-like action between the rails. The pedestal mounting brackets of the front pedestal extending above the truck rails want to assume an angular difference to each other during such loads.
Another cause of distortion occurs during turning of the truck. The tandem rear axles on the truck cause considerable resistance to turning and lateral bending of the truck frame. This distortion is termed "laddering", i.e.; one rail of the truck gets ahead of the other rail.
It has been proposed to provide some flexibility in the mounting of the pedestals that support the drum. An example is the Johnson U.S. Pat. No. 4,575,254 issued Mar. 11, 1986, in which one of the pedestal ends is free to rotate. However, being mounted above the rails, this rotation does not accommodate the binding of the tubular cross member occasioned by frame distortions caused by the scissoring and laddering action of the truck rails.
According to the present invention, spherical ball joints are provided to mount the pedestal and permit frame distortions to occur without undue resistance. If the truck frame can "move" around the pedestals because of such mounting, the pedestals can be built as a rigid assembly without trying to restrain the truck frame movement. In the case of both pedestals, the present invention enables these pedestals to provide a flat and rigid platform on which the drum drive and roller mechanisms respectively, are mounted.
Each pedestal consists of an upright frame structure, the lower ends of which are connected to the side frame members by means of self aligning bearings. The central upper portion of the upright frame is connected by a diagonal link or strut to a separate cross member arranged forwardly thereof, the ends of the link being likewise connected by self-aligning bearings. By utilizing a "C" section as a cross member and arranging it so the shear center of the member can serve as the point of attachment of the lower end of the strut, the load path of the strut will pass through the shear center and will not cause the cross members to rotate.
This invention permits a lighter truck mixer frame design because it reduces the torsional reactionary forces that are carried by the truck chasis main rails laddering and scissoring under irregular road conditions. This is a decided advantage because any decrease in weight enables the mixer to haul larger concrete payloads without violating street or highway weight limits.